Each year there are approximately 50,000 newly diagnosed brain tumors. Chemotherapy is established to be important in the treatment of newly diagnosed and recurrent brain tumors. Laboratory based studies have established that DNA alkylation plays a key role in the initiation of cellular death by chemotherapeutic agents. In order to achieve a better understanding of this process in brain tumor therapy; we propose to measure the formation of DNA abducts in intracerebral (ic.) Tumors treated with alkylating chemotherapeutic agents currently being evaluated for the treatment of brain tumors. To achieve this goal we propose to Aim 1. Optimize a dissociation enhanced lanthanide fluoroimmunoassay (DELFIA) method fo the quantitatation of O6 -methyldeoxguanosine (O6 -MedG). The levels of N7 -methyldeoxguanosine (N7 - MeG) will be determined by electrochemical detection. We will measure the levels of O6 -MedG and N7 -MeG formed in U-87MG cells grown as ic. Tumors in athymic rats treated with temozolamide (TMZ). In these tumors, we will investigate the relationships between levels of O6 -MedG and N7-MeG formed and route of administration, treatment dose and agent and number of treatments. The levels of these alkylation products formed in the ic. tumors will be compared with the levels formed in the contralateral hemisphere and in normal tissues. These methodologies will provide ea unique approach for preclinical analysis of alkytating chemotherapeutic agents in treatment of brain tumors. Aim 2. We will develop a poly clonal antiserum to the dG-dC crosslink (1- [N3-2'deoxycytidly], 2-[N1-2; -DEOXYGUANOSYL]-Ethane) formed by BCNU. Using this antiserum, we will optimize a DELFIA method for the quantitation of the dG-dC crosslink. Aim 3 Investigate the formation of the dG-dC crosslink, O6-(2-hydroxy ethyl) deoxyguanosine (O6- HOEtdG) and N7 - (2-hydroxy ethyl) deoxyguanosine N7-HOEtG. Athymic rats bearing U-87MG ic. Tumors will be treated with either BCNU SarCNU or mitozolamide. The formation of dG-dC crosslink, O6-HOEtdG and N7-HOEtG will be quantitated. We will examine the relationships between levels of these alkylation products and treatment agent, dose and. Number of treatment. These studies will be the first to investigate the formation of BCNU derived DNA abducts in a ic. Brain tumor model.